The present invention relates to refrigeration equipment and specifically applies to all chiller applications including water cooled, air cooled and process applications. More particularly, the present invention relates to refrigeration equipment including a coalescing oil sump demister. The present invention is described with respect to centrifugal compressors but is applicable to all compressors having a refrigerant/lubricant mixture.
Compressors are used to compress a refrigerant. In refrigeration equipment, such as centrifugal compressors, refrigerants have an affinity for oil and therefore tend to mix with oil. This mixing has the undesirable effects of reducing the utility of both the oil and the refrigerant. Specifically, oil can be lost to the refrigeration system if oil mist or droplets are carried in the vent gas stream.
Demisting is the process by which oil is separated from a refrigerant-oil vapor mixture. A system for "demisting" oil from the refrigerant-oil mixture is disclosed in, for example, U.S. Pat. No. 4,359,329 to Willeitner. In such a system, cylindrically shaped sleeves with wire mesh arranged therein are used to remove oil from a refrigerant-oil vapor mixture. The oil removed then falls due to gravity. Willeitner does not, however, disclose a housing located within the oil sump, a coalescing filter, or a filter located within the housing. Additionally, in Willeitner, oil passes downstream of the demisters.
A coalescing oil filter is disclosed in U.S. Pat. No. 4,213,307 to Watson. A coalescing filter medium has an upstream side in communication with an inlet and a downstream side in communication with a refrigerant gas outlet and an oil outlet. When the coalescing filter of Watson is used, oil in the bottom of the filter housing passes through an oil outlet. The oil then passes through a line to an oil pump. The oil pump then returns oil through yet another line to the interior of the gear and bearing housing. Watson does not, however, disclose a filter housing located in the oil sump interior or a filter located within such a housing.
U.S. Pat. No. 5,685,699 to Holmes et al. shows a demister 10 which keeps oil mist from the transmission chamber 30 from passing to the impeller. The demister 10 is located high in the transmission chamber 30 above the gears 31, 34 and precedes a vent pipe 65 leading to the suction housing cavity 67. Details of the demister are not provided.
The above-described conventional demisters have the undesirable features of a limited demister filter surface area, the need for a complex system for transporting oil from a demister to an oil sump, and allowing oil to pass through the demister filter, thereby making the demisting process inefficient.